Malignant mesothelioma is a rare and highly aggressive cancer, resistant to usual curative treatments. The development of the malignant pleural mesothelioma is mostly linked to a prolonged exposure to asbestos fibres and dusts (Kazan-Allen et al., Lung cancer, 2005, 49S1:S3-S8; Robinson et al., Lancet, 2005, 366:397-408). Melanoma is a malignant tumour that develops in melanocytes and can spread to the entire body when it is not treated. Although it represents one of the least frequent types of skin cancers, it is responsible for the most skin cancer-related deaths (Chin, L. et al., Genes Dev. 2006 20: 2149-2182). Lung adenocarcinomas are the most common kind of lung cancer, both in smokers and non-smokers and are one of the most common causes of cancer death (Travis, W. D. et al., J Thorac Oncol., 2011, 6(2), 244-285).
No strategy currently proposes a significant curative opportunity for several aggressive cancers such as malignant mesotheliomas, melanomas and lung adenocarcinomas.
Their prognoses are very poor and they are relatively refractory to all conventional treatment modalities, such as chemotherapy, radiotherapy and/or surgery. There is thus a pressing need for the development of new clinical approaches.
Cancer virotherapy is widely regarded as a new alternative for the treatment of cancers that are resistant to conventional anti-cancer therapies (Boisgerault N et al., Immunotherapy, 2010, march 2(2), 185-199). Oncolytic virotherapy has demonstrated multimodal antitumour mechanisms in both pre-clinical and a few phase I clinical anti-cancer treatments (Lech, P J and Russell, S J; Expert Review of Vaccines, 2010, 9(11):1275-1302; Galanis et al., Cancer Research, 2010, 70(3):875-882), and also in in vitro investigations (Gauvrit, A et al., Cancer Research, 2008, 68 (12), 4882-4892). Compared with cell-transfer immunotherapy, virus-vaccines have the advantage of conferring personalised anti-cancer immunity simultaneously with cytoreduction without the requirement for personalised manufacture. Additionally, virus-vaccines can be engineered to delete immunosuppressive viral components and to insert transgenes that enhance antitumour cytotoxicity and immunity (A. Gauvrit et al., Cancer Research, 2008, 68 (12), 4882-4892).
Measles virus (MV) is a non-segmented single-stranded, negative-sense enveloped RNA virus of the genus Morbilivirus within the family of Paramyxoviridae. The non-segmented genome of MV has an antimessage polarity, which results in a genomic RNA which is neither translated in vivo or in vitro nor infectious when purified. This virus has been isolated in 1954 (Enders, J. F. and Peebles, T. C., 1954, Proc Soc Exp Biol Med, 86(2): 277-286), and live-attenuated vaccines have been derived from this virus since then to provide vaccine strains, and in particular from the Schwarz/Moraten strain.
Transcription and replication of non-segmented (−) strand RNA viruses and their assembly as virus particles have been studied and reported especially in Fields virology (3rd edition, vol 1, 1996, Lippincott-Raven publishers—Fields B N et al.). Transcription and replication of MV do not involve the nucleus of the infected cells but rather take place in the cytoplasm of said infected cells. The genome of MV comprises genes encoding six major structural proteins from the six genes (designated N, P, M, F, H and L) and the additional two-non structural proteins from the P gene, the C and V proteins. The gene order is the following: 3′, N, P (including C and V), M, F, H, and L large polymerase protein at the 5′ end (FIG. 1A). The genome further comprises non-coding regions in the intergenic region M/F; this non-coding region contains approximately 1000 nucleotides of untranslated RNA. The cited genes respectively encode the leader peptide (I gene), the proteins of the nucleocapsid of the virus, i.e., the nucleoprotein (N), the phosphoprotein (P), and the large protein (L), which assemble around the genome RNA to provide the nucleocapsid. The other genes encode the proteins of viral envelope including the hemagglutinin (H), the fusion (F) and the matrix (M) proteins. The MV C protein is coded by the polycistronic P gene, it is a small (186 amino acids) and basic protein, localised both in the cytoplasm and in the nucleus (Bellini, W. J. et al., J. Vivol., 1985, 53:908-919). The role of this viral protein, described as a MV virulence factor, is not yet well understood. To determine the role of the MV C protein, a recombinant wild-type MV strain lacking expression of the C protein, based on the highly pathogenic IC-B strain and generated by using a reverse genetics system, has been used. It was suggested that the MV C protein could be involved in the assembly of viral particles, in the virus protein expression and in the delay of apoptosis of infected cells in order to establish a long term MV infection (Takeuchi, K. et al., J. Vivol., June 2005, 7838-7844). Although it has been reported that the MV C protein inhibits the interferon antiviral response (Shaffer, J. A. et al., Virology, 2003, 315:389-397), another study reached the opposite conclusion (Takeuchi, K. et al., J. Vivol., June 2005, 7838-7844), thereby confirming that the function of the MV C protein has not yet been well established.
Among human viruses that deserve to be tested as oncolytic agents, live-attenuated MV vaccine presents a number of advantages. Administered to hundreds of millions of children during 30 years, it is the safest and most widely used human paediatric vaccine. Attenuated strains of MV infect a large number of cell types and preferentially the transformed cancer cells. This is due to the use by MV of CD46 as a receptor frequently over-expressed in cancer cells to resist to the complement-dependant killing by natural killer cells (Naniche, D. et al., J Vivol, 1993, 67(10): 6025-6032; Dhiman, N. et al., Rev Med Vivol, 2004, 14(4): 217-229), whereas wild-type MV uses preferentially SLAM (CD150) (Tatsuo, H. et al. Nature, 2000, 406(6798):893-897; Anderson, B. D. et al., Cancer Res., 2004, 64: 4919-4926; Schneider, U. et al., J Virol., 2002, 76: 7460-7467). Interestingly, MV exhibits natural antitumour properties by specifically targeting cancer cells without infecting the healthy ones. Thus, MV demonstrates an unquestionable safety profile for application in future therapeutic protocols.
The oncolytic properties of wild-type MV are well known to a person skilled in the art (Mayo Foundation for Medical Education and Research, U.S. Ser. No. 07/854,928). Recently, clinical trials were initiated to investigate the capacity of an Edmonston MV strain to treat ovarian, glioblastoma, non-small lung cancer and multiple myeloma (see http://clinicaltrials.gov, measles and cancer keywords). The use of MV vaccines, either recombinant or chimeric, as vaccination vectors has also been described (WO2004/000876, WO2004/076619, WO2006/136697, and WO2008/078198).
This technology has also been proposed to the immuno-oncolytic treatment of mesothelioma (Gauvrit, A. et al., Cancer Research, 2008, 68 (12), 4882-4892). Accordingly, International Patent Application WO2009/047331 described both the oncolytic and immuno-adjuvant properties of the live-attenuated Schwarz strain of MV vaccine on a panel of epithelioid mesothelioma tumour cells. Using a rescued Schwarz strain of MV vaccine produced from an infectious cDNA clone, it was shown that MV-infected mesothelioma cells induced spontaneous monocyte-derived dendritic cell (Mo-DC) maturation and a tumour antigen-specific response.
The potential advantages of oncovirotherapy over conventional treatments include the property to induce an immune response including not only higher on-target specificity against cancer antigens (tumour associated antigens), and thus a better safety margin but also prolonged effect due to immune memory, and thus preventing relapse and metastasis. Indeed, it has been demonstrated that an immune-specific response and memory are developed after administration of MV at the site of cancer cells, in the presence of antigen-presenting cells (Masse, D. et al., Int. J. Cancer, 2004, 111(4), 575-580); Liu et al., Molecular therapy: the journal of the American Society of Gene Therapy, 2010, 18(6):1155-1162). It was demonstrated that the antitumour activity of the Schwarz MV strain acts through multiple mechanisms, including oncolysis, induction of tumour immunogenic apoptosis (danger signal expression associated with cell death) and virus-mediated syncytium formation (Gauvrit, A. et al., Cancer Res, 2008, 68(12), 4882-4892). In addition, the released tumour associated antigens and the inflammation resulting from viral replication have also been suggested to break the immunotolerance to tumours and induce anticancer immunity.
Despite an efficient infection, some MV-infected malignant tumour or cancer cells resist to cell death induction. Hence there is a need for the development of viruses that would help to overcome this type of resistance, and thus improve and extend the specific cell death induction of malignant tumour or cancer cells.
Dendritic cell (DC) precursors are divided into monocyte-derived dendritic cells (Mo-DCs) and plasmacytoid dendritic cells (pDCs), which display different functional properties. pDCs are a subset of DCs involved in the antiviral immune response due to their expression of Toll-like receptors (TLR) specialised in the recognition of viral nucleic acids (TLR7, TLR9) (Gilliet, M. et al., Nat Rev Immunol., 2008, 8:594-606). They respond to a wide range of viruses (inter alia influenza A virus, herpes simplex virus, HIV) in terms of activation and maturation by producing large amounts of type-I interferon (IFN-α, -β, -ω). They are also able to present viral antigens to CD8+ and CD4+ T cells when they are infected by a virus (Fonteneau, J. F. et al., Blood, 2003, 101:3520-3526) and to cross-present viral antigens from virus-infected cells to CD8+ T lymphocytes (Di Pucchio, T. et al., Nat Immunol., 2008, 9:551-557; Lui, G. et al., PLoS One, 2009, 4:e7111). It has also been shown that pDCs could play a beneficial role in the immune response against tumours (Drobits, B. et al., J Clin Invest., 2012, 122:575-585; Liu, C. et al., J Clin Invest., 2008, 118:1165-1175). As an example, in a mouse melanoma model, pDC activation and antitumour immune response were observed inside tumours after topical treatment with the TLR7 ligand, imiquimod (Drobits, B. et al., J Clin Invest., 2012, 122:575-585). As MV is single-stranded RNA (ssRNA), the inventors have hypothesised that pDCs could be able to detect the MV infection of tumour cells, because of their intravacuolar TLR7 expression which recognises single-stranded RNA.